Animated explainers can take a long time to produce. The amount of time for a project is based directly on the complexity of the animation required and on the rounds of edits that are necessary. Be sure to state what your ideal length would be, it you have a script written or voice over produced. State what your desired turnaround time is. If you have examples, or ideas, be sure to include them as well. The more info for the producer the better. Keep in mind that rush productions will increase the cost.